This invention relates to medical devices and specifically to devices which are effective in the treatment of hydrocephalus. More specifically, the invention relates to an implantable drainage valve for draining excess cerebrospinal fluid ("CSF") from the brain to a drainage area elsewhere in the body.
Hydrocephalus is a condition in which the body, for any of several reasons, is unable to relieve itself of excess CSF collected in the ventricles of the brain, resulting in increased epidural and intradural pressures. This in turn causes adverse physiological effects including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Various types of drainage valves have been used in the treatment of hydrocephalus. Generally, these valves allow for the controlled drainage of excess CSF from the brain to a suitable drainage area in the body such as the peritoneal cavity, for example. CSF drainage valves include check valves, servo valves and combinations thereof. Check valves operate by opening when the fluid pressure differential between their inlet and outlet openings exceeds a certain predetermined threshold value.
Noted drawbacks in the use of simple check valves include their failure to compensate for the differences in liquid column height which result when the patient stands after lying in a recumbent position. In these situations, the differential fluid pressure normally increases by reason of the resulting increased vertical height of the fluid column existing between the head and the selected drainage location. Though such an increase in differential pressure is normal, a simple check valve will typically respond by opening and thereby allowing undesired hyperdrainage of the ventricular spaces which may result, for example, in a potentially serious hematoma. Accordingly, it is desirable to provide a hydrocephalus pressure relief valve which is effective in shunting CSF in response to abnormal intracranial pressures while avoiding hyperdrainage in the event of normal variations in fluid pressures.
One solution proposed to mitigate such drawbacks in simple check valves has been to add an additional valve body in series with the original check valve. In this arrangement, a check valve is combined in series with an additional valving mechanism intended to prevent the valve from opening in response to normal CSF pressure variations. The typical check valve includes a ball valve held in a tapered valve seat under the force of a compression spring. When CSF pressure exceeds a predetermined threshold, the fluid pressure unseats the ball to allow fluid to pass through the valve. A second valve body is provided in series with the check valve to prevent CSF drainage in those situations where the check valve has opened in response to normal fluid pressure differentials.
One example of such a second valve body includes a second tapered end seat with a second ball valve seated therein to control the flow of fluid from the check valve through the second body. Spherical weights are positioned within the second valve body to hold the second ball valve in its valve seat under the influence of gravity when the device is vertical. In this arrangement, the additional spherical weights maintain the valve in a closed condition in those instances where the check valve might open in response to the normal pressure differentials experienced by the valve, such as when the patient rises to a standing position. These valves, however, are expensive, requiring the accurate machining of at least two tapered valve seats, and, the inclusion of additional valve parts have made such valves rather bulky, requiring lumbar implantation. Finally, combined valves of this type may experience undesirable dynamic or ballistic effects when the patient engages in jerking movements such as running or jumping. These dynamic effects may adversely interfere with the proper operation of the valve.
The present invention overcomes the problems of the prior art and meets the aforementioned goals by providing a pressure relief valve which prevents excessive drainage of CSF in the event of normal increases in differential pressure and which is inexpensive to manufacture and is designed for cranial implantation. In the preferred embodiment, the valve is provided in a cylindrical housing including a single ball valve seated in a tapered valve seat and retained therein under the force of a compression spring. At least one spherical weight is positioned in the housing to coact with the ball valve and compression spring to keep the valve in a closed condition when the valve experiences normal variations in CSF pressure.
Possible ballistic or dynamic effects are further minimized in the valve design of the present invention due to the direct mechanical relationship between the closure member, the compression spring and the spherical weights housed within the cylindrical housing. An adjustment screw is provided in association with the housing and the spherical weights to set the valve to open at a predetermined fluid pressure.
It is accordingly an object of the present invention to provide a device for the relief of excess cerebrospinal fluid pressure and useful in the treatment of hydrocephalus and the like.
It is another object of the present invention to provide a drainage valve suitable for cranial implantation and useful in the treatment of hydrocephalus.
It is another object of the present invention to provide a drainage valve useful in the treatment of hydrocephalus and which prevents excessive drainage of CSF in the event of normal increases in differential fluid pressure such as when a patient stands after lying in a recumbent position.
These and other objects of the present invention will be more clearly understood upon consideration of the remainder of the disclosure, including the detailed description of the preferred embodiment and the appended claims.